Hi Greger, I found the exact problem which have been paining me. 1) the nated Sip-proxy; its sending the route headers as if it forgets it staying behind the Nat.and sending the call as some thing like this invite 99106883(a)81.21.33.35 <mailto:99106883@81.21.33.35> ----this is my SER - server record<192.168.1.100 <http://192.168.1.100>>------- this is nated sip-proxy address contact<192.168.1.100 <http://192.168.1.100>>-----contact to this address only SER-server is frowarding the call to pstn Gateway as it recieves and just rewriting the host name. and the other problem(I think) 2) PSTN Gateway. even when call connects it is adding the strict route headers as it recieves from SER-server and when it sends 200 0k after connecting the call it is not getting back or SER-server is also not getting back the "ACK" from the nated proxy because the nated proxy itself add the contact header as (private-ip ) ofcourse it is following strictly the SIP-PROTOCOL so,these are the two problems i found , Some providers are providing calls to this nated sip-proxy -------> How ???? Why the SER-server is also not following the path where "INVITE" message came ????? How to stop the Nated Sip-proxy to stop sending the headers in "INVITE"message not including the record route or contact headers in the message --- ?????? Or is there any way to do in SER-server itself ( majorly prefered) not to contact private ip-address and to follow the next address which is NAT-IP ---??????? (I think its foolish question )---> Or is there any way to get registered another sip-proxy in location database.----??????? Please suggest me some thing to get out of this problem. Thank You. Regards, Ravi.